**2.3 Conclusions**

On the basis of this study, it is expected that the UASB reactors packed with steel elements may be applicable to treat UF whey permeate to produce biogas with high CH4 content. The COD removal efficiency, biogas productivity and CH4 content in biogas were enhanced by 11.4 - 17.0% (p<0.05), 1.67 - 2.15 m3 m3 d-1 (p<0.05), 8.3 - 17.2% (p<0.05), respectively, in the UASB reactor packed with steel elements compared to the control reactor performances. In this work, the maximum biogas production rate was 8.22 L d-1 in the reactor containing additional iron medium in contrast to about 4.2 L d-1 in the control reactor. Total phosphorus removal efficiency obtained in RFe was higher by 58.4 - 77.7% than in R0 (p<0.05). High iron concentration in the anaerobic granular sludge was not contributed to inhibit the activity of methanogenic bacteria. It should be pointed that during anaerobic corrosion process a protective layer on the steel surface can be formated to decrease phosphorus removal efficiency.
